Aerial roots

If a root is above ground, how can it take in water? The Lord Howe pandan has evolved a solution: it has developed grooves that function like aqueducts, according to Victoria University researcher Matt Biddick.

Pandans are found on tropical and subtropical coasts around the Pacific. They have weak trunks, but grow tall by sending roots down from the canopy that form stilts when they reach the ground.

Most pandans grow to less than five metres high, but a Lord Howe Island species, Pandanus forsteri, grows to more than 15 metres, so it takes years for the aerial roots to reach the ground.

Without being able to draw moisture from the earth, the roots gather it by other means. The leaves of P. forsteri are shaped like gutters, and funnel water toward the trunk. Then, grooves on the top surface of the roots channel the water to the roots’ tips, where spongy absorptive tissue carries the collected rainwater to the rest of the plant.